What happens when a charged insulator is placed near an uncharged neutral metallic conductor? I know it attracts each other because of charging by induction (electrons redistribute). But would the redistribution of electrons in the metal result in a net electric field inside the conductor or no net electric field? I'm curious to know what and why.
[Physics] Neutral conductor and charged insulator brought near each other
chargeconductorselectric-fieldselectrostaticsequilibrium
Related Solutions
The localization or delocalization of the excess charge in conductors and insulators can be understood in a way similar to the uncharged case using band theory. Please refer to the first diagram in:
http://en.wikipedia.org/wiki/Work_function
For simplicity let us consider the zero temperature case. The Fermi energy $E_F$ can be thought of as a level which separates the occupied states from the empty states. Now, as you may know, the Fermi energy in a metal would lie in a band. In other words, in metals you have half filled bands; this is why electrons, near the Fermi energy, are delocalized in metals. In semiconductors, however, the Fermi energy lies within the band (as shown in the figure) leaving all the bands either completely filled or empty. As a result, the electrons are localized.
Since the Fermi energy separates the filled and empty states, it can, intuitively, be thought of as the surface of a fluid in a container; the fluid is analogous to the electrons in the system. Now, as you add or remove the fluid, its surface will either rise or drop respectively. Changes in the Fermi energy can be visualized in the same way. There is, however, one caveat: the vacuum energy $E_{VAC}$ will also change, in addition to $E_F$, as excess charge is introduced. $E_{VAC}$ is considered as the energy at which the electron is no longer bound to the solid. If the solid is charged positively or negatively, it will be harder or easier for the electron to escape respectively. As a result, one only considers changes in work function $\Phi$ or electron affinity $E_{ea}$. The former is often used in the case of metals and the latter in the case of semiconductors or insulators.
To sum it all up, excess charges will result in changes in $\Phi$ and $E_{ea}$. After these changes have occurred, by the introduction of access charges, it's a question of where the Fermi energy sits. Depending on that, the electrons will either be localized or delocalized. For a reasonable value of excess charge the Fermi energy will only move by a small amount, and will still typically lie in one of the bands or in the band gap in a metal or insulator respectively. This is why the excess charge will be delocalized, and cover the entire surface of the metal; whereas the excess charge will be localized in an insulator.
If you want to get a better feel for how $E_F$, $E_{VAC}$, $\Phi$, and $E_{ea}$ change as excess charge develops on metals, insulators, and semiconductors, you can take a look at chapter 2 of:
What keeps electrons on a negatively-charged conductor from leaving?
It is a quantum mechanical phenomenon. Wherever there exists an electric field potential there exist energy levels , i.e. stable orbital locations which can be occupied by an electron.
How does this happen?
Even the simple Hydrogen atom has a negative ion state, an anion. This is because the potential describing the hydrogen atom, neutral, still has many levels in which the electron can transition, and there exists a probability for an extra electron to be attracted to one of these levels, though one would have to solve the problem " two electrons one proton" energy levels. Even in the ground state the electron orbital has a p state probability, which means that the shape allows regions in space where the positive charge is open to attract other negative charges. These shapes are what allow the molecular bonding into H2.
In neutral atoms/molecules orbitals have shapes given by the complicated spin states necessary for the binding into molecules and solids, and there exist spill over forces that can be attractive to free electrons, i.e. have energy levels that are open to extra electrons. The stability then is guaranteed unless extra interactions occur, as described in the other answers.
One tends when speaking of bulk matter, as in conductors in the question, to forget the underlying quantum mechanical state, but if at the molecular and atomic level there do not exist stable quantum mechanical solutions with energy levels , then there would be no bindings. One speaks of surface tension and work functions etc to describe the many body effect of the underlying quantum mechanical state. The basic stability is due to the energy levels every time.
Best Answer
The answer is that no matter how the charges in the insulator are arranged, the electric field inside the conductor will still be zero. Imagine an insulator, which only contains a single electron. If placed above a conductive plate, the positive charges in the conductor will be attracted to it. The negative charges in the conductor will be repelled.
Now apply Gauss' law to a region inside the conductor (green box). Since all the charges will have rushed to the surfaces in response to the electron, the center will contain no charges. If no charges are enclosed, there will be no electric field at its surface.
None of this changes if more electrons are added to the insulator or if their spatial distribution changes. This will cause the charges at the surface of the conductor to rearrange themselves, but there still won't be any inside the conductor. The field there remains zero.